From: Christophe Leroy <christophe.leroy-2tlSp11Fh4xulxpn9UvDqw@public.gmane.org>
To: Arnd Bergmann <arnd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Ard Biesheuvel <ardb-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
Rich Felker <dalias-8zAoT0mYgF4@public.gmane.org>,
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Linux-sh list <linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
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Will Deacon <will-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
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Brian Cain <bcain-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
Helge Deller <deller-Mmb7MZpHnFY@public.gmane.org>,
X86 ML <x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Ru
Subject: Re: [PATCH 08/14] arm64: simplify access_ok()
Date: Wed, 16 Feb 2022 19:43:22 +0000 [thread overview]
Message-ID: <07050857-c9d2-bab2-2191-8d244d6f7708@csgroup.eu> (raw)
In-Reply-To: <CAK8P3a2VfvDkueaJNTA9SiB+PFsi_Q17AX+aL46ueooW2ahmQw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
Le 15/02/2022 à 10:12, Arnd Bergmann a écrit :
> On Tue, Feb 15, 2022 at 9:17 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>> On Mon, 14 Feb 2022 at 17:37, Arnd Bergmann <arnd@kernel.org> wrote:
>>> From: Arnd Bergmann <arnd@arndb.de>
>>>
>>
>> With set_fs() out of the picture, wouldn't it be sufficient to check
>> that bit #55 is clear? (the bit that selects between TTBR0 and TTBR1)
>> That would also remove the need to strip the tag from the address.
>>
>> Something like
>>
>> asm goto("tbnz %0, #55, %2 \n"
>> "tbnz %1, #55, %2 \n"
>> :: "r"(addr), "r"(addr + size - 1) :: notok);
>> return 1;
>> notok:
>> return 0;
>>
>> with an additional sanity check on the size which the compiler could
>> eliminate for compile-time constant values.
>
> That should work, but I don't see it as a clear enough advantage to
> have a custom implementation. For the constant-size case, it probably
> isn't better than a compiler-scheduled comparison against a
> constant limit, but it does hurt maintainability when the next person
> wants to change the behavior of access_ok() globally.
>
> If we want to get into micro-optimizing uaccess, I think a better target
> would be a CONFIG_CC_HAS_ASM_GOTO_OUTPUT version
> of __get_user()/__put_user as we have on x86 and powerpc.
>
There is also the user block accesses with
user_access_begin()/user_access_end() together with unsafe_put_user()
and unsafe_get_user() which allowed us to optimise user accesses on
powerpc, especially in the signal code.
Christophe
next prev parent reply other threads:[~2022-02-16 19:43 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-14 16:34 [PATCH 00/14] clean up asm/uaccess.h, kill set_fs for good Arnd Bergmann
2022-02-14 16:34 ` [PATCH 01/14] uaccess: fix integer overflow on access_ok() Arnd Bergmann
2022-02-14 16:58 ` Christoph Hellwig
2022-02-14 16:34 ` [PATCH 02/14] sparc64: add __{get,put}_kernel_nocheck() Arnd Bergmann
2022-02-14 16:34 ` [PATCH 03/14] nds32: fix access_ok() checks in get/put_user Arnd Bergmann
2022-02-14 17:01 ` Christoph Hellwig
2022-02-14 17:10 ` David Laight
2022-02-15 9:18 ` Arnd Bergmann
2022-02-15 10:25 ` Greg KH
2022-02-14 16:34 ` [PATCH 04/14] x86: use more conventional access_ok() definition Arnd Bergmann
2022-02-14 17:02 ` Christoph Hellwig
2022-02-14 19:45 ` Arnd Bergmann
2022-02-14 20:00 ` Christoph Hellwig
2022-02-14 20:01 ` Linus Torvalds
2022-02-14 20:17 ` Al Viro
2022-02-15 2:47 ` Al Viro
2022-02-14 20:24 ` Linus Torvalds
[not found] ` <CAHk-=wgYu67OwP4LhcrPdDVxv2mOsx-Xsc2DKoVW6GZwKFtOYQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2022-02-14 22:13 ` David Laight
2022-02-14 16:34 ` [PATCH 05/14] uaccess: add generic __{get,put}_kernel_nofault Arnd Bergmann
2022-02-14 17:02 ` Christoph Hellwig
2022-02-15 0:31 ` Al Viro
2022-02-15 13:16 ` Arnd Bergmann
2022-02-14 16:34 ` [PATCH 06/14] mips: use simpler access_ok() Arnd Bergmann
2022-02-14 16:34 ` [PATCH 07/14] uaccess: generalize access_ok() Arnd Bergmann
2022-02-14 17:04 ` Christoph Hellwig
[not found] ` <20220214163452.1568807-8-arnd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2022-02-14 17:15 ` Al Viro
2022-02-14 19:25 ` Arnd Bergmann
2022-02-15 10:58 ` Mark Rutland
2022-02-14 16:34 ` [PATCH 08/14] arm64: simplify access_ok() Arnd Bergmann
2022-02-14 21:06 ` Robin Murphy
2022-02-15 8:17 ` Ard Biesheuvel
2022-02-15 9:12 ` Arnd Bergmann
2022-02-15 9:21 ` Ard Biesheuvel
2022-02-15 9:39 ` Arnd Bergmann
[not found] ` <CAK8P3a0NTqK_m7q909d8FN6is8k4_u3zeckC9XOrjEi7kqSvmg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2022-02-15 10:39 ` Mark Rutland
2022-02-15 10:37 ` Mark Rutland
[not found] ` <CAK8P3a2VfvDkueaJNTA9SiB+PFsi_Q17AX+aL46ueooW2ahmQw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2022-02-16 19:43 ` Christophe Leroy [this message]
2022-02-15 9:30 ` David Laight
2022-02-15 11:24 ` Mark Rutland
2022-02-15 11:07 ` Mark Rutland
2022-02-14 16:34 ` [PATCH 09/14] m68k: drop custom __access_ok() Arnd Bergmann
2022-02-15 0:37 ` Al Viro
2022-02-15 6:29 ` Christoph Hellwig
2022-02-15 7:13 ` Al Viro
2022-02-15 10:02 ` Arnd Bergmann
2022-02-15 13:28 ` David Laight
2022-02-14 16:34 ` [PATCH 10/14] uaccess: remove most CONFIG_SET_FS users Arnd Bergmann
2022-02-14 17:06 ` Christoph Hellwig
2022-02-14 19:40 ` Arnd Bergmann
2022-02-14 16:34 ` [PATCH 11/14] sparc64: remove CONFIG_SET_FS support Arnd Bergmann
2022-02-14 17:06 ` Christoph Hellwig
2022-02-16 13:06 ` Arnd Bergmann
2022-02-15 0:48 ` Al Viro
2022-02-16 13:07 ` Arnd Bergmann
2022-02-14 16:34 ` [PATCH 12/14] sh: " Arnd Bergmann
2022-02-14 16:34 ` [PATCH 13/14] ia64: " Arnd Bergmann
2022-02-14 16:34 ` [PATCH 14/14] uaccess: drop set_fs leftovers Arnd Bergmann
2022-02-15 3:03 ` Al Viro
2022-02-15 7:46 ` Helge Deller
2022-02-15 8:10 ` Arnd Bergmann
[not found] ` <20220214163452.1568807-1-arnd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2022-02-14 17:35 ` [PATCH 00/14] clean up asm/uaccess.h, kill set_fs for good Linus Torvalds
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